Petroleum refining and petrochemical processes frequently involve acid gases which are present as impurities in numerous industrial fluids, i.e., liquid and gas streams. These acid gases include hydrogen halides such as HCl, HF, HBr, HI and mixtures thereof.
For example, one of the key processes in refining petroleum is catalytic reforming. In the catalytic reforming process, a light petroleum distillate or naphtha range material is passed over a noble metal catalyst to produce a high octane product. Hydrogen is a by-product of the catalytic reforming process, and a portion of the byproduct hydrogen is recycled to the reaction zone to maintain catalyst stability. Typically, the noble metal reforming catalyst is promoted with chloride which, in the presence of hydrogen, results in the production of a small amount of hydrogen chloride. Thus, the net byproduct hydrogen withdrawn from the catalytic reforming process generally contains a small amount of hydrogen chloride.
Similarly, in a process for the dehydrogenation of light iso-paraffins to produce iso-olefins, the promoting of the noble metal catalyst with chloride will produce a net hydrogen stream containing small amounts of HCl. The net hydrogen produced in the catalytic reforming process and the dehydrogenation process is generally used in sensitive downstream catalytic processes. In addition, there are other hydrocarbon and chemical processes in which small amounts of HCl are generated and carried away in gas or liquid streams.
Even small amounts of gaseous HCl present in the net hydrogen can seriously interfere with the operation of downstream processes which use the hydrogen and can cause corrosion problems in the equipment such as pipes, valves, and compressors which convey hydrogen. Generally, HCl in gas or liquid hydrocarbon streams must be removed from such streams to prevent unwanted catalytic reactions and corrosion of process equipment. Furthermore, HCl is considered a hazardous material and releasing the HCl to the environment must be avoided.
Existing sorption processes for removing HCl from hydrocarbon-containing streams typically involve passing the hydrocarbon-containing fluid stream over a sorbent, which is disposed in a fixed bed. There are various formulations that are currently used as sorbents to remove chlorides from various streams.
For example, some sorbents comprise alumina. However, the alumina sorbents generally have a low capacity and the spent material had a high reactivity (of HCl on the surface) tending to form “green oil.” Typically, these green oils are green or red in color and generally contain chlorinated C6 to C18 hydrocarbons and are believed to be oligomers of light olefinic hydrocarbons. The presence of green oils in the fixed sorbent bed fouls the sorbent bed and results in the premature failure of the sorbent. When this fouling occurs, often costly measures are required to remove the spent sorbent from the bed. Furthermore, the chloride content of the green oils on the spent sorbent makes disposal of the spent sorbent an environmental problem. While the exact mechanism of green oil formation is unknown, it is believed that green oils are formed by catalytic reaction of aluminum chloride or HCl with the hydrocarbon. Green oil formation remains an unresolved industry problem during the removal of HCl from hydrocarbon streams.
Some alumina sorbents have been doped with various additives, such as alkali or alkaline earth elements, to improve the performance of the chloride scavengers. See, U.S. Pat. Nos. 3,557,025; 3,943,226; 4,639,259; 5,505,926; and 5,935,894.
Furthermore, some chloride sorbents comprise a zeolite which acts as a molecular sieve to trap the chloride compounds within the pores of the zeolite. See, U.S. Pat. No. 8,551,328. However, the chloride capacity per gram is lower, making the use of same impracticable.
Finally, some chloride sorbents utilize metal oxide with a binder such as alumina or others which, like the activated alumina sorbents, remove chloride compounds via an acid-base reaction. While presumably effective for their intended uses, it is believed that such sorbents have a lower capacity due to the use of a binder which takes away from the amount of active material that may be in such compositions.
The appropriate chloride sorbent may depend on the particular applications of type of use. For example, catalytic reforming processes can often include continuous catalyst regeneration which produces gas streams that are non-fouling, dry, and can be subjected to long contact times with a sorbent. It is believed that chloride adsorbents with high capacities would be useful in such applications.
It is desirable to discover new sorbents which can be used in such processes. It is further desirable to discover and develop sorbents with different properties, such as activity and selectivity.